Retaining walls are built to hold back earth or soil that would otherwise move or slide forward and down. There are various types of retaining walls, including gravity, piling, cantilever and anchored. Gravity walls hold the soil back mainly through their own weight and lean back into the retained soil for additional stability. Conventional gravity retaining and two-sided decorative walls made with natural stone are typically assembled and built on location.
Natural stone walls are traditionally built with or without mortar. Dry stacked (mortar-less) fieldstone walls are very popular in the New England area and are usually decorative in nature. Retaining fieldstone walls that need to be more structural in nature or withhold high earth or soil pressures are usually built with mortar. In harsher northern climates where freeze-thaw cycles are the culprits for many failed or failing retaining walls, it is even more crucial for the stone retaining wall to have proper drainage and other engineering components to ensure adequate retaining capacity.
Constructing a stone wall on location is costly, time consuming and leaves the site cluttered with piles of stone and other masonry construction materials and debris. It is also subject to weather conditions, which are unpredictable.
Some of tried to overcome some of the foregoing issues by building modular stone walls that can be include a plurality of panels built in advance, that are delivered and assembled at the site. Such modular retaining wall systems can use natural stone and various types of modular or panel systems are known for building walls (some of which are mounted or anchored onto existing structures) that attempt to imitate a natural stone wall as well as a number of wall systems of precast textured or treated concrete made to look like real stone.
Many of the prior approaches for making modular stone walls have problems when put into practice, and none address the key components of a modular wall that is completely seamless in appearance, made of natural stone, structurally and securely connected, and sufficiently made to serve as a retaining wall.
For example, in U.S. Patent No. 5,624,615, Sandorff, a method of manufacturing modular stone panels is described where stones are set in a mold and concrete is cast only on rear face of walls—leaving the outer front sides exposed between gaps resembling mortar joints. When the panel is erected, the resulting wall has the appearance of a masonry wall that was assembled stone by stone using mortar. This method uses embedded coil-threaded structures and reinforcing rods to lift and join the panels together. The resulting wall does not come together seamlessly (e.g., has clearly visible vertical joints) and requires cap plates to hide the top of the wall, which is exposed concrete. The weep holes created by rods are not connected to anything and in reality, become blocked with loose dirt and soil almost instantly rendering them useless in dissipating groundwater to prevent hydrostatic pressure buildup. Furthermore, in practice, the coil-threaded rods are not strong enough to safely lift and flip upright (without damage to the stone face of the wall) an extremely heavy wall panel that would weigh around 200 lbs (90 kg) per square foot. In practice, walls lifted as described in this patent would hang at about a 30 degree angle and could not be lowered vertically into adjacent panels as required. Also, given the weight of each wall panel and difficulty maneuvering the same, to perfectly align and join wall panels using the “tongue and groove” system described is impossible in practice.
In patent application publication US 2005/0281626, to Smith, disclosed is a floating natural mortared stone modular wall and method for constructing the same. This system does not address aesthetic or structural requirements for a natural stone retaining wall and will also have visible vertical seams at each wall panel connection. And the resulting wall will need to have an exposed concrete top since the system allows each wall panel to move independently of one another in a vertical motion and has no structural engineering components, such as drainage required for a gravity retaining wall.